Oil boiler problem?

[markbu]

Hi
I have a 14 year old Myson Velaire Vitesse Oil boiler located downstairs which heats HW & CH. The boiler was serviced about a year ago. Upstairs is the hot water tank, water pump and two motorised valves. In the loft is the header tank. I have 15 radiators in the house all with TRV's. There is no thermostat (that i'm aware of)

In the morning everything comes on as programmed (CH should be on during the whole day), but after about an hour the boiler turns off and the radiators downstairs start to get cold. However the water pump doesn't switch off. The radiators upstairs stay warm for quite a few hours even though the boiler is off. The house gets colder and colder and but the boiler won't turn back on. In the end I manually turn the programmer to off and the water pump shuts down. Once everything seems cool I can turn the programmer on again and the boiler starts up with about a 50% chance to continue the cycle described above.

I checked the motorised valves and they appear to be functioning i.e. they are opening and closing.

Any ideas??

 

[AlanE]

they are opening and closing.

Might well be opening and closing ok but are the internal microswitches being operated? If not boiler will not work.

Sounds as if the valve heads are either defective or the valve itself is stiff and not opening fully.

 

[MANDATE]

Is your problem related to CH only or does boiler refuse to start using HW only.
Solenoid coils on the oil pump do go faulty in such a way that they may function when cool but go open circuit when heated. It's a break in the coil winding, but the wire is still touching so it works until the heat causes expansion and gap between wire so it no longer works. But may work again after cooling down. So you need to check solenoid

 

[oilhead]

If you do not have to press the burner control reset, then the problem is with the ontrols, either boiler thermostat, room thermostat or motorised valves. Basic electrical checking should enable you to identify the fault.
first check for continuity on boiler stat, then room stat, then check for power out of motorised valve heads. If pump continues to run, then these should be O.K. Does your velaire vitesse have a post purge PCB fitted? This can cause trouble, but is easily by-passed for checking.

 

[snb]

check that the pump is actually pumping after the hour or so. Could be that it's own windings are failing, or that it has pumped up carp from system and blocking impeller.